The present invention relates to polymers which contain substituted indenofluorene derivatives as structural unit, to substituted indenofluorene derivatives, to a process for the preparation of the polymers according to the invention, to mixtures (also known as blends) and solutions which comprise the polymers according to the invention, and to the use of the polymers according to the invention in electronic devices, in particular in organic electroluminescent devices, so-called OLEDs (OLED=organic light emitting diode).
In the past, predominantly small molecules were employed as useful components, for example as phosphorescence emitters, in organic electroluminescent devices. The use of small molecules in organic electroluminescent devices (SMOLEDs) enables good colour efficiencies, long lifetimes and the requisite low operating voltages. However, the disadvantage of such systems is the complex production. Thus, for example, the deposition of layers of small molecules requires complex processes, such as, for example, thermal coating processes, which results in a limited maximum device size.
For some time, conjugated polymers having the corresponding properties have therefore been used for opto-electronic applications, since they can be applied easily and inexpensively as a layer by rotation coating or print coating. In addition, systems of this type usually have a long lifetime. Conjugated polymers have already been investigated intensively for some time as highly promising materials in OLEDs. OLEDs which comprise polymers as organic materials are frequently also known as PLEDs (PLED=polymer light emitting diode). Their simple production holds the promise of inexpensive production of corresponding electroluminescent devices.
PLEDs consist either only of one layer, which is able to combine as far as possible all functions (charge injection, charge transport, recombination) of an OLED in itself, or they consist of a plurality of layers which comprise the respective functions individually or partially combined. For the preparation of polymers having the corresponding properties, the polymerisation is carried out using different monomers which take on the corresponding functions.
Thus, it is generally necessary for the generation of all three emission colours to copolymerise certain monomers into the corresponding polymers. In order to generate white light by light mixing, light in the three colours red, green and blue is required. In order to ensure high light efficiency, triplet emitters (phosphorescence) are preferred to weaker-light singlet emitters (fluorescence). Conjugated polymers are only suitable as host materials for red- or yellow-emitting triplet emitters, but not for triplet emitters having relatively high energy (blue- or green-emitting triplet emitters), since the low triplet energies of the conjugated polymers quench the emission from any triplet emitters having relatively high energy (relatively short wavelengths).
In order to circumvent the said problem of quenching, it is possible to employ non-conjugated or partially conjugated polymers. However, these have to date the disadvantage that the lifetime of such systems is unsatisfactory. Thus, for example, poly-N-vinylcarbazole is a known system for a triplet emitter in the green region. However, opto-electronic devices produced therefrom have extremely short lifetimes.
Thus, with the exception of triplet emitter polymers which emit in the deep-red region, no polymers having a long lifetime and high emission efficiency have been provided to date.
In order to solve this problem, WO 02/04543 has already proposed polymers whose conjugation is interrupted by the incorporation of diphenylfluorene into the polymer backbone. WO 05/061181, EP 1589595, WO 97/31048 and WO 97/20877 likewise propose spirobifluorene as conjugation-interrupting unit in the polymer backbone. However, polymers containing these units have low solubility in organic solvents. It is thus virtually impossible to use inexpensive production processes, such as rotation coating and print coating, for the production of organic electroluminescent devices.